Monaz: Hello, I'm Monaz Mehta, editor in the Cochrane Editorial and Methods department. Coronavirus disease 2019, or COVID-19, has spread quickly throughout the world, and Cochrane is producing reviews to help decision makers respond to the pandemic. In April 2020, we published the rapid review of the effects of using ash for cleaning hands when soap and water are not available. In this podcast, Lars Jørgensen from the Nordic Cochrane Centre spoke to his colleague there, Asger Paludan-Müller, about the review.

Lars: So, Asger, you and your group have done this systematic review of ‘ash for cleaning hands’. Can you tell us a little about why you did it?

Asger: Well, as we all know, proper hand hygiene is one of the most important measures for preventing the spread of infectious diseases, COVID-19 included. Unfortunately, about 40% of the world’s population don’t have access to soap and running water, so low-cost alternatives are badly needed. Ash is used in some parts of the world, and has been recommended by several NGOs, but we were not aware of any systematic review of its potential benefits and harms.

Lars: I see, so a systematic review was needed. Which types of study did you plan to include?

Asger: We expected that there would be few, or no, randomized trials, so we decided to also look for observational studies such as cohort studies, case-control studies and controlled before-after studies. We were mainly interested in studies examining clinically relevant outcomes, such as bacterial or viral infections, hospital admissions and harms that had examined different ways of cleaning hands.

Lars: Makes sense, so were you able to identify any relevant studies?

Asger: Yeah, our search yielded 58 unique records, including one randomized trial. Overall, we ended up including 14 studies described in 19 articles, with five non-randomised trials, four cross-sectional studies, three prospective cohort studies, and one case-control study, as well as the randomized trial.

Lars: Ok, so it sounds like you had quite a lot of data to work with.

Asger: Unfortunately, no. Many of the studies did not really differentiate between the effects of ash and soap, and we found no studies which directly examined our pre-specified outcomes. Two observational studies looked at infections, but none of them confirmed the diagnosis with laboratory tests. One looked at clinically made diagnoses of diarrhoea, but diarrhoea can be caused by things other than bacteria or virus. The other looked at self-reported symptoms of reproductive tract infection, but again there may be other causes for such symptoms. We also identified four studies that took a bacterial count after handwashing using different materials, but this is a surrogate outcome, and it’s not clear how clinically relevant it is. Finally, we judged that all the studies with relevant data were at either critical or high risk of bias.

Lars: That’s clearly disappointing. So how would you sum up your review and where can people find it?

Asger: Well, based on the few trials, the surrogate outcomes and the high risk of bias, we’re not able to make any firm conclusions at this time about the benefits and harms of hand cleaning using ash. We need large randomized trials with clinically relevant outcomes to see if ash really is a useful alternative to soap and water. It’s important that people are aware of this and I’m pleased that the review is freely available online. If people go to Cochrane Library dot com, and type in a simple search for 'ash and hand cleaning', they will find it.